ActiveState's Komodo IDE is another editing powerhouse aimed at helping people build and debug not just PHP but Node.js, Python, Perl, TCL and Ruby.
The newest version, 7.0, adds more collaborative editing so that several people can work on the same document at the same time, presumably without doubling the number of bugs being created. There's also a mechanism that uses ActiveState's Stackato platform to deploy your code to the cloud or a local machine.
The editor offers many features for working with the marked-up files, including code highlighting, code suggestions and code folding. The editors work with all of the HTML and CSS, helping build the final web view. There's a visual editor that works well.
The debugger includes a number of options for doing more than just stopping. It can count how many times the breakpoints are hit and even execute a bit of code at the breakpoint. This may be the biggest help for tricky problems buried deep in the call stack.
The documentation talks about the "breadth" of the IDE, and PHP sometimes feels a bit lost in the shuffle. PHP seems to be just another language, while Python and Ruby seem to get more attention. There were several places where the documentation was out of sync with the machine, prompting me to scramble to the Web for answers. Komodo also wants to integrate with the local PHP server to handle debugging. I couldn't use just any local version of PHP that might be more helpful.